Methods of forming polycrystalline bodies using rhombohedral graphite materials

ABSTRACT

Methods of synthesizing polycrystalline bodies using rhombohedral graphite materials are disclosed and described. One procedure includes providing a particulate graphite source having a majority of carbon atoms oriented in a rhombohedral polytype configuration. The particulate graphite source can be shaped into a desired shape having a porosity from about 0% to about 30%. A sufficient amount of heat and pressure can be applied to the desired shape to form diamond and consolidate the diamond into a polycrystalline body.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/900,037, filed Jul. 26, 2004 which application claims thebenefit of U.S. Provisional Patent Application No. 60/490,170, filedJul. 25, 2003, each of which are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates to methods for synthesizingpolycrystalline bodies. Accordingly, this invention involves the fieldsof chemistry, materials science, metallurgy, and geology.

BACKGROUND OF THE INVENTION

The production of synthetic diamond is a process that has received muchattention over the years and been sought for a variety of industrialapplications. Today a number of diamond synthesis processes are known,several of which have been successfully commercialized. Examples ofvarious diamond synthesis methods can be found in U.S. Pat. Nos.2,947,611; 3,030,188; 3,238,019; 3,401,019; 4,377,565; 4,483,836;5,209,916; 5,614,258; and 6,315,871, each of which are incorporatedherein by reference.

At the basis of many diamond synthesis processes is the application of atremendous amount of heat and pressure to a carbon source, such asgraphite. One method of particular interest involves the conversion ofgraphite to diamond via a shock wave produced by an explosion. Thisprocess was introduced during the 1960's, and is described in U.S. Pat.No. 3,238,019. Generally speaking, the process involves placing a carbonsource such as graphite in close proximity to an explosive element whichis then detonated. The shock waves produced by the explosion apply apressure and a temperature to the graphite that is adequate to convertthe graphite to diamond.

While many of the above-referenced processes have been successfullycommercialized, most remain expensive and inefficient. For example,despite the fact that the shock wave synthesis method has beencommercially used by DuPont deNemours, Co. for several decades now, itis still little better than about 15% efficient. Therefore, the cost ofdiamond particles yielded by the process is quite expensive remaining atapproximately $2.00 per carat or more.

As a result, methods for efficient and cost effective synthesis ofdiamond and other superabrasives continue to be sought through on-goingresearch efforts.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides methods of improvedefficiency for synthesizing superabrasive particles from a superabrasiveprecursor. The superabrasive precursor can include a source materialdistributed in a metal matrix. The source material can be a rhombohedralgraphite source having a majority of carbon atoms oriented in arhombohedral polytype configuration. The rhombohedral graphite source issuitable for synthesis of diamond particles. Alternatively, the sourcematerial can be hexagonal boron nitride which is suitable for synthesisof cubic boron nitride particles. A shock wave can be passed through thesource material that is sufficient to convert the source material tosuperabrasive particles.

In one aspect, at least about 80% of the carbon atoms of the graphitesource can be oriented in a rhombohedral polytype configuration. In yetanother aspect, the carbon atoms of the graphite source can besubstantially all oriented in a rhombohedral polytype configuration.

The rhombohedral polytype graphite can be obtained by using variousmethods. However, in one aspect, the rhombohedral graphite can beprovided by dissolving carbon in a molten metal, and then solidifyingthe molten metal to form the superabrasive precursor. While a number ofmetal types may be used as the carbon solvent, in one aspect, the metalcan be selected from the group consisting of Fe, Co, Ni, Mn, Cr, andsemi-alloys or alloys thereof. In another aspect, the metal can be Fe.Further, while the amount of carbon added to the molten metal can benearly any amount desired, in one aspect, the amount of carbon can besufficient to substantially saturate the metal with the carbon.Alternatively, additional carbon can be added beyond the saturationpoint of the metal for carbon such that a mixture of undissolved carbonand molten metal saturated with dissolved carbon is formed.

Once the carbon is dissolved in the molten metal and has been convertedto the rhombohedral polytype of graphite, the metal can be solidified inpreparation to receive a shock wave. Optionally, prior tosolidification, the metal can be shaped into a number of configurationsthat facilitate easy handling thereof, and which can in some respectscontribute to the ease of converting graphite to diamond. Further someshapes can allow use of various shock wave sources which may otherwisebe ineffective. Examples of such shapes include without limitation,bars, sheets, rods, etc. Additionally, the solidified metal containingthe rhombohedral graphite can be cut into sections, or otherwise reducedin size or shaped, following solidification, but prior to application ofthe shock wave.

In yet another alternative embodiment, the superabrasive precursor canbe provided by forming a mixture of powdered metal and powdered sourcematerial. For example, a mixture of hexagonal graphite and powderedmetal can be mechanically mixed in a device sufficiently to formrhombohedral graphite from the hexagonal graphite. A non-limitingexample of a suitable device can be an attritor, such as those used toform mechanical alloys or semi-alloys.

The shock wave that is applied to the superabrasive precursor can befrom any source that produces a shock wave sufficient to convert thesource material to superabrasive particles. Typically, the amount ofpressure that must be produced by the impact to effect the conversion ofgraphite to diamond is from about 5 GPa to about 100 GPa. In anotheraspect, the pressure can be from about 8 GPa to about 20 GPa. However,this range may vary somewhat depending on a variety of factors that willbe recognized by those of ordinary skill in the art, such as the sizeand thickness of the solidified metal containing the carbon, etc. In oneaspect, as is known in the art, the shock wave can be supplied by anexplosion. In another aspect, the shock wave can be provided byphysically impacting the superabrasive precursor.

Once the conversion from the source material to superabrasive particlehas taken place, the superabrasive particles can be harvested from thesolidified metal. Those of ordinary skill in the art will recognize avariety of mechanisms for separating the metal from the superabrasiveparticles, such as acid dissolution of the metal, or electrolytic orgaseous removal of the metal.

In some instances, it can be advantageous to remove the graphite fromthe metal once it has been converted to the rhombohedral form, andbefore the shock wave is applied to convert it to diamond. By so doing,it is possible to greatly improve the efficiency of making diamond toolsor masses by converting the rhombohedral graphite into diamond as partof the tool fabrication process. In this manner the extra step ofheating and pressing the graphite simply to convert the graphite todiamond can be avoided, and the overall process of producing diamondtools, or a polycrystalline diamond mass is greatly improved.

Accordingly, the present invention additionally provides a method ofmaking a diamond body that includes: a) providing a particulate graphitesource having a majority of carbon atoms oriented in a rhombohedralpolytype configuration; b) shaping the particulate graphite source intoa desired shape for the mass, said desired shape having a porosity fromabout 0% to about 25%; and c) applying a sufficient amount of heat andpressure to the graphite source to convert the graphite particles todiamond and to consolidate the diamond particles into the diamond body.Notably, the processing options and limitation as recited above for theproduction of diamond are applicable in the process of making suchdiamond aggregates as well. Those of ordinary skill in the art willrecognize a number of additional processing steps and ingredients thatcan be added to the basic process outlined above. However, in oneaspect, the method of making diamond aggregates can additionally includeadding a binder agent to the graphite particles prior to heating andpressing the particles. In another aspect, the binder agent can be Co.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome clearer from the following detailed description of the invention,taken with the accompanying claims, or may be learned by the practice ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of hexagonal graphite having a stackedgraphene plane sequence (ABAB) as is known in the prior art.

FIG. 2 shows a side view of rhombohedral graphite having a stackedgraphene plane sequence (ABCABC) and the structural changes that occurduring the process of converting such graphite into diamond inaccordance with one embodiment of the present invention.

FIG. 3 shows a side view of lonsdaleite graphite having a stackedgraphene plane sequence of (AaA), and the structural changes that occurduring the process of converting such graphite into lonsdaleite inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

A. Definitions

In describing and claiming the present invention, the followingterminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a carbon source,” or “the carbon source,” includes reference to one ormore specific sources of carbon, and reference to “an extractionprocess” includes reference to one or more of specific processes forextraction.

As used herein, “rhombohedral graphite,” and “rhombohedral polytypegraphite” may be used interchangeably, and refer to an allotropic formof graphite with an ABCABC stacking sequence of graphene layers.Rhombohedral graphite is well known in the chemical arts and iscontained in the IUPAC Copendium of Chemical Terminology (2^(nd) ed.1997), which is incorporated herein by reference.

As used herein, “hexagonal graphite,” and “2H graphite” may be usedinterchangeably, and refers to an allotropic form of graphite with anABAB stacking sequence of graphene layers. Hexagonal graphite is wellknown in the chemical arts and is contained in the IUPAC Copendium ofChemical Terminology (2^(nd) ed. 1997), which is incorporated herein byreference.

As used herein, “shock wave” refers to a wave of significant energy,such as a large amplitude compression wave produced by an impact orexplosion.

Concentrations, amounts, solubilities, volumes, weight percents, andother numerical data may be presented herein in a range format. It is tobe understood that such range format is used merely for convenience andbrevity and should be interpreted flexibly to include not only thenumerical values explicitly recited as the limits of the range, but alsoto include all the individual numerical values or sub-ranges encompassedwithin that range as if each numerical value and sub-range is explicitlyrecited.

For example, a range of 0.01 to 20 should be interpreted to include notonly the explicitly recited limits of 0.1 and 20 but also to includeindividual values within that range, such as 0.5, 1.0, 5, 10, 15, andsub-ranges such as 0.5-5, 5-10, 10-15, etc. This interpretation appliesto open-ended ranges reciting only one numerical value as well, such as“less than about 20,” and should apply regardless of the breadth of therange or the characteristic being described.

B. The Invention

The present invention involves methods for making syntheticsuperabrasive particles such as diamond or cubic boron nitride from asuperabrasive precursor. The superabrasive precursor can include asource material distributed in a metal matrix. The source material canbe a rhombohedral graphite source suitable for synthesis of diamondparticles. Alternatively, the source material can be hexagonal boronnitride which is suitable for synthesis of cubic boron nitrideparticles. A shock wave can be passed through the source material thatis sufficient to convert the source material to superabrasive particles.

In accordance with the present invention, the source material can haveadjacent crystallographic planes wherein individual atoms are aligned ina configuration which allows for conversion to a superabrasive materialupon application of a sufficiently energetic shock wave. Typically, thisrequires that individual atoms have corresponding atoms in adjacentcrystallographic planes to which they can be bonded.

Referring now to FIG. 1 there is shown a section of hexagonal graphite.This is the most common isotropic form of graphite which is arrangedwith graphene layers in the ABA arrangement. Accordingly, only half ofthe carbon atoms find corresponding carbon atoms in the adjacentgraphene planes. As such, the graphite, even if deformed by a shock waveof significant force will spring back to its original configuration.Common sources of hexagonal graphite can have up to about 15 wt %rhombohedral graphite.

By contrast, FIG. 2 shows a section of rhombohedral graphite and theresultant conversion to diamond upon application of a shock wave withsufficient energy. As can be seen, this isotropic form of graphite isarranged with graphene layers in the ABCABC arrangement, so that eachcarbon atom in each layer has a corresponding carbon atom in one of thetwo adjacent graphene layers. As such, upon application of a shock waveof sufficient energy, the graphite is converted to cubic diamond asshown.

Accordingly, a method for synthesizing diamond can include providing agraphite source having a majority of carbon atoms oriented in arhombohedral polytype configuration, and passing a shock wave throughthe graphite that is sufficient to convert the graphite to diamond.Notably, it is desirable to have as much of the graphite as possibleconfigured with carbon atoms oriented in rhombohedral form. In oneaspect, at least about 80% of the carbon atoms of the graphite sourcecan be oriented in a rhombohedral polytype configuration. In anotheraspect, substantially all of the carbon atoms in the carbon source canbe oriented in a rhombohedral configuration.

Alternatively, the source material can be hexagonal boron nitride (hBN)source. Hexagonal boron nitride has a stacking sequence of AaAa which isconducive to formation of cubic boron nitride upon application of ashock wave. The hBN source can comprise or consist essentially of hBN.In most cases, it can be desirable to provide an hBN source whichconsists essentially of hBN.

Referring to FIG. 3 is shown one form of hexagonal graphite that iscapable of forming diamond via shock wave synthesis. This isotropic formknown as lonsdaleite has an AaA graphene planar arrangement, whichresults in all carbon atoms having a corresponding carbon atom inadjacent graphene planes. Therefore, upon application of a shock wavewith sufficient energy, diamond will be formed. However, because of thelonsdaleite configuration, the diamond formed is hexagonal rather thancubic. Notably, lonsdaleite is rare occurring naturally only at certainmeteor impact sites. However, researchers have developed methods whichallow synthetic production of lonsdaleite which may make this form ofgraphite a potentially useful starting material for use in the presentinvention.

Thus, the methods of the present invention can be useful for producingsuperabrasive materials from source materials which have an interplanararrangement wherein each atom within a plane have a corresponding atomin an adjacent plane. Thus, planar arrangements of ABCABC and AaA can beused while a planar arrangement of ABA such as that found in hexagonalgraphite is generally not suitable.

Applicant has identified that hexagonal graphite can be converted torhombohedral graphite upon dissolution with certain metal catalysts.Accordingly, in one aspect, the rhombohedral graphite used in thepresent invention can be provided by dissolving carbon in a molten metaland then solidifying the molten metal to form the superabrasiveprecursor. While not wishing to be bound by any particular theory, it isthought that the ability of the molten metal to convert hexagonalgraphite into a rhombohedral polytype is due to the attraction ofelectrons in the graphite by empty shells in the d-orbitals of themetal. Because graphene planes are held together by weak Van der Waalsforces, the attraction of unpaired or “dangling” electrons in carbonatoms at the outer edges of the carbon mass is sufficient to shuffle thegraphene planes into the rhombohedral configuration.

A variety of metals are deemed suitable for use in the methods of thepresent invention. However, in one aspect, the metal matrix can comprisea carbon solvent. For example, common carbon solvents can be a memberselected from the group consisting of Fe, Co, Ni, Mn, Cr, andsemi-alloys or alloys thereof. In another aspect, the metal can compriseor consist essentially of Fe. In another aspect, the metal can be Co. Inone aspect of the present invention, the metal matrix can besubstantially free of copper or other non-carbon solvent metals.

As a practical matter, it should be noted that while any amount ofcarbon from nearly any carbon source can be added to the molten metal,that it is preferable to add enough carbon so that the molten metalbecomes substantially saturated with the carbon. In this manner, a moreefficient diamond yield is achieved from application of a shock wave. Asa general guideline, the typical saturation point of carbon in carbonsolvent metals is less than about 5 wt %. For example, carbon can bedissolved in iron up to about 4 wt %, while nickel and cobalt candissolve up to about 3 wt % carbon.

Additionally, in some embodiments it can be desirable to add excesscarbon such that a mixture of undissolved carbon and metal havingdissolved carbon therein is formed. In this manner the content ofrhombohedral graphite can be increased per volume of superabrasiveprecursor, thus increasing yields of diamond per volume of precursor.Thus, in accordance with an aspect of the present invention, additionalcarbon can be included in the superabrasive precursor. In one aspect,the carbon content of the superabrasive precursor can be from about 1 wt% to about 20 wt %, inclusive of dissolved and undissolved carbon. Inone additional aspect, the undissolved carbon content of thesuperabrasive precursor can be from about 8 wt % to about 15 wt %. Onenon-limiting example of a suitable superabrasive precursor is highcarbon cast iron.

Further, as a practical matter it should be noted that while thesuperabrasive precursor can be solidified into nearly any shape ordesign, that certain designs or configurations are preferential, and canbe somewhat determinative of the additional processing steps to betaken. However, in one aspect, the molten metal having the carbondissolved therein can be shaped into either a bar, a sheet, or a rodprior to solidification. In one aspect, the configuration can be a rod.

Additionally, the molten metal may be further shaped or treated aftersolidification, but before application of the shock wave. For example,in one aspect, the solidified metal can be cut into sections, such asdiscs or segments.

In another alternative embodiment of the present invention, thesuperabrasive precursor can be provided by forming a mixture ofparticulate metal and powdered source material. For example, aparticulate metal and hexagonal graphite can be provided and thenmechanically mixed sufficiently to form rhombohedral graphite from thehexagonal graphite. Typically, this mechanical mixing can beaccomplished using a high shear mixer such as an attritor commonly usedfor forming mechanical alloys, i.e. semi-alloys. The mechanical mixingcauses partial melting of the particulate metal sufficient to at leastpartially convert the hexagonal graphite to rhombohedral graphite.Although this embodiment can result in a somewhat lower conversion thanwhen using molten metal, the results can be satisfactory. Additionally,conversion of hexagonal to rhombohedral graphite can be increased bylengthening the mechanical mixing time. The mixture can be formed withalmost any content of graphite; however, a graphite content of fromabout 15 wt % to about 70 wt %, and often about 50 wt %.

In yet another alternative embodiment, the rhombohedral graphite can beformed using deposition techniques such as arc evaporation of graphiteor sputtering of graphite under specific conditions. For example, U.S.Pat. No. 4,273,561, which is incorporated by reference herein, describesseveral exemplary processes for forming rhombohedral graphite which canbe used in connection with the present invention.

When synthesizing superabrasive cBN particles, the superabrasiveprecursor can further comprise additional catalyst materials such asalkali metals, alkali earth metals, and compounds thereof. Severalnon-limiting specific examples of such catalyst materials can includelithium, calcium, magnesium, nitrides of alkali and alkali earth metalssuch as Li₃N, Ca₃N₂, Mg₃N₂, CaBN₂, and Li₃BN₂.

The shock wave used in the method of the present invention can beproduced by various sources, such as explosions, chemical blasts,physical impact upon the solidified metal, etc. The only proviso withrespect to the shock wave is that it must provide a sufficient amount ofenergy to cause the rhombohedral graphite to “pucker” as show in FIG. 2and become converted to diamond or to cause the hBN to rearrange to formcBN. In one aspect, the shock wave can provide a pressure of, or anenergy equivalent to a pressure of, from about 5 GPa to about 100 GPa.In another aspect, the pressure can be from about 8 GPa to about 20 GPa.Those of ordinary skill in the art will recognize additional specificpressure settings, or additional amounts of shock wave energy that aresufficient to achieve a particularly desired result upon implementationof the methods of the present invention. Further, those of ordinaryskill in the art will recognize equipment and reaction configurationswhich may be useful in harnessing the energy of an explosion, orapplying a physical impact to allow a shock wave of sufficient energy topass through the rhombohedral carbon and effect the conversion todiamond. In addition, the shock wave can be applied under ambientatmospheric conditions such that no special atmosphere or vacuum isnecessary.

In one aspect of the present invention, a hammer, anvil, press, or thelike can be used to apply the physical impact. In embodiments whichinvolve physical impact, it can be desirable to form the superabrasiveprecursor into thin sheets to improve transmission of the impact energythroughout the precursor. Additionally, the superabrasive precursor canbe placed on a heated surface. For example, a thin, e.g., less than 1mm, sheet of superabrasive precursor can be laid on a heated surfacesuch as a heated tungsten carbide substrate. An anvil or hammer can thenbe impacted on the superabrasive precursor with sufficient force toconvert at least a portion of the source material to superabrasiveparticles. Typically, this process can require repeated physical impactin order to achieve valuable yields of diamond or cBN.

In accordance with the present invention, yields of diamond cantypically exceed about 20%, and can often range from about 25% to about70%. Most often, diamond yields can be from about 25% to about 60%.However, yields outside of this range can also be achieved, depending onthe metal matrix material, conditions, carbon source material, or thelike.

An additional advantage to utilizing the solidified molten metal as themedium in which the shock wave is applied to the graphite is the absenceof pores, and high material density of the metal. As a result, the shockwave is able to pass through the graphite at a greater speed.Furthermore, the reduction or absence of pores minimized temperatureincreases due to the shock wave, and therefore reduces the incidence ofthe newly formed diamond becoming back converted to amorphous carbon orgraphite. This temperature reduction is at least partially due toincreased thermal conductivity resulting from a decrease in porosity. Insome cases, the temperature can be less than about 1700° C. As a generalguideline, the porosity of the superabrasive precursor can be less thanabout 30% and in most cases is from about 0% to about 25%. When therhombohedral graphite is provided by using a molten metal, the porosityof the superabrasive precursor can preferably be less than about 5%. Ina most preferred embodiment, the superabrasive precursor can besubstantially non-porous.

Once diamond is formed, it can be removed from the solidified moltenmetal in order to be useful for incorporation into a diamond tool. Thoseof ordinary skill in the art will recognize a variety of ways in whichthe diamond can be separated from the metal, such as by acid dissolutionof the metal, and electrolytic and vapor transport of the metal awayfrom the diamond. The recovered superabrasive particles can be in themicron size range and in some cases can be in the nanometer size range.Typically, these superabrasive particles can have a nanocrystallinestructure regardless of the particle size. As such, these particles tendto have beneficial wear characteristics such as reduced scratching andhigh material removal rates. This is at least partially due to aspectthat when the superabrasive particles fracture, the particles fracturealong the nano-scale crystalline planes rather than on the roughermacro-scale. Typically, the superabrasive particles produced from moltenmetal containing rhombohedral graphite result in nanometer sizedparticles, e.g., less than about 100 nanometers.

In some aspects, it can be desirable to harvest the rhombohedralgraphite from the solidified molten metal prior to application of theshock wave force thereto. The rhombohedral graphite can be harvested inthe same or similar manner as those recited above for harvestingdiamond. Once harvested, the rhombohedral graphite can be converted todiamond by application of a shock wave as recited herein.

Additionally, the harvesting of graphite from the solidified metal priorto application of a shock wave allows the fabrication of polycrystallinediamond (PCD) bodies in a single step, rather than the traditional twostep method. Traditionally, the manufacture of a PCD body from syntheticdiamond has required that diamond particles first be produced, and thenconsolidated into the PCD. In each step significant amounts of heat andpressure are required. Accordingly, a mechanism for creating a PCD ofsynthetic diamond in a single high pressure high temperature step hasbeen sought. Such a method would reduce the costs associated with PCDproduction by perhaps more than half.

In one aspect of the present invention, a method is provided forproducing a PCD with a single high pressure high temperature step.Specifically, the steps for producing diamond as recited above arefollowed, until the step of passing a shock wave through the graphite.Prior to performing this step, the rhombohedral graphite is harvestedfrom the solidified molten metal. The graphite particulates can then beplaced in a mold and given a desired shape for the PCD. At this point,an amount of heat and pressure that is sufficient to convert thegraphite particles to diamond and to consolidate the diamond particlesinto a PCD body is applied. Those of ordinary skill in the art willrecognize appropriate pressures and temperatures, and mechanisms forproviding such, in order to attain a specific resultant PCD.

Preferably, the porosity of the desired shape is minimized. As a generalguideline, the porosity of the desired shape can be less than about 30%using cold isostatic pressing or other similar pressing processes,although porosities of less than 20% can be achieved by hot isostaticpressing, mixing particle sizes to improve packing densities, or othersimilar processes.

Of course, other ingredients typically used in the fabrication of PCDbodies, such as a binder agent can be added to the mold and used in thepresent single high pressure high temperature method for manufacturing aPCD. A wide range of ingredients that are suitable for use will berecognized by those of ordinary skill in the art. However, in oneaspect, a metal binder agent can be used. However, in one aspect, thebinder agent can be Co.

It is to be understood that the above-referenced arrangements areillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements. Thus, while the presentinvention has been described above with particularity and detail inconnection with what is presently deemed to be the most practical andpreferred embodiments of the invention, it will be apparent to those ofordinary skill in the art that numerous modifications, including, butnot limited to, variations in size, materials, shape, form, function,manner of operation, assembly, and use may be made without departingfrom the invention as set forth in the claims.

1. A method of making a polycrystalline diamond body comprising: a)providing a particulate graphite source having a majority of carbonatoms oriented in a rhombohedral polytype configuration; b) shaping theparticulate graphite source into a desired shape for the polycrystallinediamond body, said desired shape having a porosity from about 0% toabout 30%; and c) applying a sufficient amount of heat and pressure tothe graphite source to convert the graphite particles to diamond and toconsolidate the diamond particles into the polycrystalline diamond body.2. The method of claim 1, wherein at least about 80% of the carbon atomsof the graphite source are oriented in a rhombohedral polytypeconfiguration.
 3. The method of claim 1, wherein the carbon atoms of thegraphite source are substantially all oriented in a rhombohedralpolytype configuration.
 4. The method of claim 1, wherein therhombohedral graphite is provided by dissolving carbon in a moltenmetal, solidifying the molten metal, and harvesting the rhombohedralgraphite from the metal.
 5. The method of claim 4, wherein the metalcomprises a member selected from the group consisting of Fe, Co, Ni, Mn,Cr, and semi-alloys or alloys thereof.
 6. The method of claim 5, whereinthe metal comprises Fe.
 7. The method of claim 4, wherein the carbon isadded to the molten metal in an amount that is sufficient tosubstantially saturate the metal with the carbon.
 8. The method of claim4, wherein the rhombohedral graphite is harvested from the solidifiedmolten metal using an acid.
 9. The method of claim 1, wherein thegraphite particles are shaped into the desired shape using a mold. 10.The method of claim 1, wherein the desired shape has a porosity of lessthan about 15%.
 11. The method of claim 1, further comprising adding abinder agent to the graphite particles prior to heating and pressing theparticles.
 12. The method of claim 11, wherein the binder agent is Co.13. A polycrystalline diamond body formed by the method of claim 1.